[RFC PATCH v4 05/39] KVM: arm64: Perform CMOs on locked memslots when userspace resets VCPUs

[Alexandru Elisei]

Userspace resets a VCPU that has already run by means of a
KVM_ARM_VCPU_INIT ioctl. This is usually done after a VM shutdown and
before the same VM is rebooted, and during this interval the VM memory can
be modified by userspace (for example, to copy the original guest kernel
image). In this situation, KVM unmaps the entire stage 2 to trigger stage 2
faults, which ensures that the guest has the same view of memory as the
host's userspace.

Unmapping stage 2 is not an option for locked memslots, so instead do the
cache maintenance the first time a VCPU is run, similar to what KVM does
when a memslot is locked.

Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
---
 arch/arm64/include/asm/kvm_host.h |  3 ++-
 arch/arm64/kvm/mmu.c              | 13 ++++++++++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index ed67f914d169..68905bd47f85 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -114,7 +114,8 @@ struct kvm_arch_memory_slot {
 
 /* kvm->arch.mmu_pending_ops flags */
 #define KVM_LOCKED_MEMSLOT_FLUSH_DCACHE	0
-#define KVM_MAX_MMU_PENDING_OPS		1
+#define KVM_LOCKED_MEMSLOT_INVAL_ICACHE	1
+#define KVM_MAX_MMU_PENDING_OPS		2
 
 struct kvm_arch {
 	struct kvm_s2_mmu mmu;
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 94fa08f3d9d3..f1f8a87550d1 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -560,8 +560,16 @@ void stage2_unmap_vm(struct kvm *kvm)
 	spin_lock(&kvm->mmu_lock);
 
 	slots = kvm_memslots(kvm);
-	kvm_for_each_memslot(memslot, slots)
+	kvm_for_each_memslot(memslot, slots) {
+		if (memslot_is_locked(memslot)) {
+			set_bit(KVM_LOCKED_MEMSLOT_FLUSH_DCACHE,
+				&kvm->arch.mmu_pending_ops);
+			set_bit(KVM_LOCKED_MEMSLOT_INVAL_ICACHE,
+				&kvm->arch.mmu_pending_ops);
+			continue;
+		}
 		stage2_unmap_memslot(kvm, memslot);
+	}
 
 	spin_unlock(&kvm->mmu_lock);
 	mmap_read_unlock(current->mm);
@@ -1281,6 +1289,9 @@ void kvm_mmu_perform_pending_ops(struct kvm *kvm)
 		}
 	}
 
+	if (test_bit(KVM_LOCKED_MEMSLOT_INVAL_ICACHE, &kvm->arch.mmu_pending_ops))
+		icache_inval_all_pou();
+
 	bitmap_zero(&kvm->arch.mmu_pending_ops, KVM_MAX_MMU_PENDING_OPS);
 
 out_unlock:
-- 
2.33.0